moving reference frame  weird results!
Hi experts,
I'm a newbie in OF and I have tried to change simpleFoam solver to achieve oscillatory reference frame, it seems that it's not a big deal but I faced weird results. I did these changes: Code:
scalar Pi = mathematicalConstant::pi; Code:
tmp<fvVectorMatrix> UEqn Any suggestion or experience in this field is really appreciated. Amir 
I'm waiting for your kind response .....

Oscillatory system (=unsteady) in steady state solver (simpleFoam)?

Quote:
I have added the transient term to UEqn., fvm::ddt(U); I have used unsteady simpleFoam instead of icoFoam because it's more stable and I could use larger time steps. Do you mean this procedure is incorrect? Amir 
Are you doing subinterations inside each time step? You can find it already done in pimpleFoam.
Best, 
Quote:
Thanks 
Hi,
to answer your question you should know if your system reaches a steady state or not. Since it is intrinsically unsteady, it might never reach one. Anyway, to use SIMPLE for unsteady calculations you should:
Best, 
Dear Alberto,
Thanks a lot for your valuable comments. Amir 
4 Attachment(s)
Dear Alberto,
I did your recommandations, but now, I have a problem in convergency. I change both pimpleFoam and also pisoFoam but convergency issues exist. I couldn't reduce initail residuals in this case, consequently, there are some differences between results and analytic solution. Do you have any recommendation about another schemes or others? I used different grids and also schemes but I couldn't achieve better convergency. 
The residual behaviour seems to show the solution is oscillating, which might indicate also a problem in the case setup.
However, you are using inconsistent numerical schemes:
Best, 
Quote:
Although the results are better know but there are some differences between this results and analytic one. Anyway, I just want to ensure that whether the solution is converged or not; you said before that in unsteady cases, initial residuals should be around 0.001. Is this criteria acceptable in such cases (oscillatory nature)? (if your answer is No; how can we ensure that the solution is converged?) Thanks again 
Yes, if you perform an unsteady calculation, the residuals should go down at each time step, until they reach the specified tolerance.
Residuals clearly won't do that in a steadystate solver, simply because your system does not have a steady state solution. Best, 
Quote:

Dear friends,
The problem is solved by implementing transientSimpleFoam solver instead of pimpleFoam or icoFoam. Thanks 
Were you having problems with pimpleFoam? If yes, what kind of problems? There should be little difference compared to a "transient SIMPLE".

Quote:
As I said before, my problem in both pimpleFoam and icoFoam was reducing initial residuals of p and U, I tried different schemes and solution controls and also time steps but I didn't achieve acceptable result particularly peak values in analytic solution; on the other hand, by transientSimpleFoam and with the same time step and schemes I achieved nice results matched with analytic one and both residuals reduced to about 0.01; I know that PISO algorithm is more precise that SIMPLE one but maybe my management for this algorithm was not efficient! Can you explain the reason of that? 
Are you using the same relaxation factors in pimpleFoam and transient SIMPLE?
If the setup is the same, they should give the same result. 
Quote:
Thanks, 
All times are GMT 4. The time now is 23:28. 